Game three of the 1932 World Series, at Wrigley Field, Chicago, on 1 October 1932. New York led the series 2-0 going in.
The bad blood
The Cubs had acquired Mark Koenig, a former Yankee, mid-season, and voted him only a half share of World Series money. The Yankee bench treated this as an insult and said so loudly and continuously.
The abuse from the Chicago dugout towards Ruth was reciprocated throughout the game.
The at-bat
Fifth inning, score 4-4, Charlie Root pitching. Ruth took a called strike, then a second, and between deliveries raised his right arm and gestured.
On the next pitch, a change-up low and away by most accounts, he hit the ball over the centre field wall into temporary seating. Contemporary estimates run around 490 feet, the longest home run recorded at that ballpark.
Lou Gehrig homered on the following at-bat.
The evidence, such as it is
Charlie Root denied it consistently and refused to be involved in a film about it. His argument was that a called shot would have earned a pitch at Ruth's head.
Gehrig said Ruth called it.
Newspaper coverage the next day is split. Some accounts describe a prediction; several detailed reports do not mention one.
Ruth's own version changed over time. Early on he was vague. Later he was categorical.
Two home movies exist, one by Matt Kandle and one by Harold Warp, both examined seriously only decades later. Both show an arm raised. Neither establishes a target.
The plausible readings
He pointed to centre field and predicted the home run.
He pointed at the Cubs dugout, which had been abusing him all afternoon.
He held up a finger to indicate one strike remaining, a gesture he was known to use.
All three are consistent with the film.
The series
New York swept it four games to nothing. Ruth was thirty-seven and this was the last World Series home run of his career.
Why it goes on a wall
Because the honest version is better than the legend. A man made an ambiguous gesture, then did something so enormous that everybody watching had to decide retrospectively what the gesture had meant, and they never finished deciding.
Nobody agrees what he meant.